Connectors are known in the art for receiving a fluid stream in a first fluid-bearing conduit and then delivering the received fluid stream to a second fluid-bearing conduit. In many cases, the fluid connection is obtained by manual alignment and coupling of separate components that comprise the connector, such as by alignment and compression of a sealing device onto a tubular device while being fitted to a receiving fitting.
The sealing device on conventional connectors is typically a ferrule having a conical frustrum exterior and a through hole. The tubular device is inserted into the through hole and the tubular device/ferrule assembly is then inserted into a receiving feature which is shaped as a complementary conical frustrum. The receiving feature is referred to as the ferrule seat. The tubular device/ferrule assembly is then forced into the ferrule seat via pressure applied by a threaded fastener.
Such an approach has several disadvantages. To effect a reliable, fluid-tight seal, the leading edge of the exterior of the ferrule must be properly oriented to the ferrule seat, which occurs only if the central axes of the ferrule and ferrule seat are perfectly coincident; both the ferrule and the ferrule seat must be fabricated to be perfectly circular; and the diameter of the through hole in the ferrule must be uniformly and adequately compressed to effect a seal between the surface of the through hole and the exterior surface of the column.
The connector and tubular device may be subject to extended periods in a variable temperature environment. For example, in gas chromatography, a connector may be employed on a tubular device in the form of a capillary column to couple a fluid stream in the column to certain devices (such as a detector) in a chromatographic apparatus. The column may be located in a convection oven wherein the temperature environment ranges from minus 70 degrees C. to 450 degrees C. Conventional connectors, when used in such an environment, are subject to expansion and contraction. As a result, the connection fails and the connector is subject to leakage. The results of such a failure include: degradation of the column via oxidation; poor quantition due to inaccurate measurement of column flow; interference effects of air at the detector; and degradation of analytes in the fluid stream as they react with the atmosphere.
One conventional approach to resolving the foregoing difficulties includes a practice of fabricating the ferrule from a compliant material. A large insertion force is then used to force the ferrule into the ferrule seat, thus causing the ferrule to conform both to the shape of the ferrule seat and to the exterior of the capillary tubing. The drawback to this approach is that a high stress is induced in the ferrule by such compression. Further, a high temperature environment will often cause such ferrule material to creep or fracture, thereby creating a fluid leak.
Another approach is to use ferrules and ferrule seats that each have a small included angle; however, a problem arises in that such a ferrule/seat combination is prone to fracture or retention (jamming) of the ferrule in the ferrule seat. Neither the ferrule nor the ferrule/seat combination is easily replaced. Thus, a routine column removal, replacement, or installation task becomes an expensive and time-consuming process.
Still another approach is to encapsulate the ferrule material in a rigid container to comprise a ferrule assembly; however, such a ferrule assembly, when subjected to extremes in temperature, appears to suffer from thermally-induced mechanical creep, which can cause a leak.
One other approach is to utilize a spring-loaded ferrule (see, e.g., U.S. Pat. No. 5,163,215) so as to compensate for thermally-induced mechanical creep. This approach has the potential to prevent failures that are due to creep-induced leaks. However, conventional apparatus have not been entirely successful because the spring, which is typically formed of metal, is subject to relaxation and annealing in a high temperature environment. Also, the conventional ferrule requires a high spring force to achieve an adequate seal, which necessitates the use of a large spring and various other parts to provide a spring assembly. Such an assembly has sufficient thermal mass that it exhibits a large heat capacity. The spring-loaded ferrule assembly then becomes an unwanted, localized thermal sink (known as a "cold spot") when positioned in a variable temperature environment. An alternative spring material, such as quartz (see, e.g., U.S. Pat. No. 4,991,883) is less subject to temperature-induced creep but still exhibits a relatively large thermal mass.
There remains a practical need for a simple, reliable, and inexpensive apparatus for receiving a fluid stream in a fluid-bearing conduit and delivering the fluid stream into a fluid flow system without incurring leaks or other failures. This need is especially apparent in connecting one or more fluid streams in an apparatus for performing high-resolution chromatography. Further, there is a need for a simple, reliable, and inexpensive apparatus for removing, replacing, or reinstalling such a fluid-bearing conduit with respect to the fluid flow system.